The circulation of a geostrophic, two-layer ocean with Ekman layers at
the top, the bottom, and the interface and driven by an anticyclonic
wind stress is determined by numerical integration. Inertial effects a
nd lateral friction are ignored. A nominal ratio of upper- to lower-la
yer thicknesses of 0.15 leads to the formation of a region in the nort
hwestern comer of the basin with lower-layer geostrophic contours that
originate from and return to the western boundary layer. This region
is referred to as unblocked. Elsewhere in the interior the lower layer
is quiescent and the system behaves like a reduced-gravity system. Th
e smallest amount of friction that could be treated by the variable gr
id procedure that was used leads to a western boundary layer with a wi
dth that is 0.1% of the width of the basin. For this limiting case flu
id in the lower layer of the unblocked region flows out of the western
boundary and turns southward and then southwestward to return to the
western boundary layer as a relatively concentrated jet near the south
ern edge of the unblocked region. The characteristic width of that jet
, in which friction is not negligible, is about 3% of the width of the
basin. In the upper layer there is a jet of comparable thickness that
flows northeastward out of the western boundary layer into the interi
or of the basin. This jet is above the lower-layer one, and the total,
barotropic transport obeys the Sverdrup balance (required by the baro
tropic vorticity equation). Thus, the model exhibits separation of the
western boundary current from the coast even when the interface does
not outcrop. That this separation occurs only for a system with very l
ittle friction may be why it has not been obtained in OGCMs, which ten
d to be rather viscous. Two approximate, analytical models are propose
d. One is semiempirical and makes use of a linear approximation to the
calculated scatterplot of potential vorticity and pressure in the low
er layer of the unblocked region. The other is based on the assumption
that the width of the lower-layer jet approaches zero as bottom frict
ion diminishes toward zero. The main features of the circulation that
was obtained numerically are captured by these approximate analytical
models. A comparison with the results of the quasigeostrophic treatmen
t of Ierley and Young is also given. The present analysis supports the
Ierley-Young conclusion that the western boundary layer does not just
respond passively to the interior flow but that it affects the interi
or flow directly.